1. Field of the Invention
The present invention concerns a chemical for cleaning an aluminium surface. In more detail, it is a cleaning agent for the purpose of removing the lubricant and press oil from an aluminium or aluminium alloy container which remaining thereon after the forming work together with aluminum powder residues (smut); it can further function to reduce contamination and corrosion of cleaning apparatus.
2. Description of the Prior Art
Aluminium or aluminium alloy made containers are usually manufactured through a draw-forming process called drawing and ironing. In the forming work, lubricant or press oil is coated on the metal surface and after the forming, aluminium powder remains adhered on the inner and outer sides of the container.
In general, a container thus formed is surface cleaned, then receives a chemical conversion coating and painting before practical usage.
The surface of the container made of aluminium or its alloy should be made perfectly clean to avoid the existence thereon of contaminants that may hinder the subsequent process of conversion coating or render the container unusable. For this purpose, one measure commonly in use is acid cleaning of the aluminium surface to remove aluminium powder or similar substances from the aluminium container surface. Acid cleaning is done at a temperature from 50.degree. to 80.degree. C. to remove or dissolve away aluminium powder and to take away lubricant or oil used for forming.
Another method is seen in Jap. Pat. Publication Sho 52-22330 (1977), Jap. Laid-open Pat. Sho 61-106783 (1986) etc. wherein an acidic cleaning liquid is proposed which contains ferric ion and thereby can reduce the corrosion of cleaning apparatus.
Problems may arise from the abovementioned first case of acid cleaning in that the heat exchanger is subject to accelerated corrosion by the acid at the heating pipes for cleaning liquid as well as at the conveyor where contact abrasion is constantly taking place.
In order to prevent the apparatus from being corroded by such acid cleaner, chromic acid or chromate has been used. However, use of chromate ion is problematic as it is hazardous.
In the latter case of acid cleaner containing ferric ion, a problem arises from the ferric ion which may adhere onto outer wall of cleaning apparatus where iron rust color develops and the apparatus becomes dirty.
Particularly in the case of a container formed from aluminium or its alloy which is used as a beverage can, the apparatus is required to be specifically clean and neat from a hygienic point of view.